<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>外边距margin</title>
    <style>
        .box1{
            width: 200px;
            height: 200px;
            border: 1px red solid;
            /*margin: 25px;*/
        /*    设置居中效果*/
            margin: 0 auto;
        }
    </style>
</head>
<body>
<div class="box1">

</div>
</body>
</html>
